修复 Studio 失败测试并新增合并门禁

把丢失的 box 录像放回 apps/studio/tests/data/，修掉第 3 节 3–10 号与两处过时测试桩，
注册 timing 标记并让根目录收集零错误；新增 tools/gate.ps1 与可选的 pre-push 钩子。
验证：studio 524 通过 19 跳过、shared 467 通过 18 跳过、ui_check 632 项 0 失败、gate.ps1 退出码 0。
细节见 docs/test-repair-plan.zh.md。

README.md

@@ -12,7 +12,7 @@ Both shipped apps are **PySide6** — Qt's **LGPLv3** binding. PyQt5's free opti
 **GPLv3-or-commercial**, which is why the studio was migrated off it: a closed-source
 product would otherwise need a licence purchase. The rule is enforced, not just
 documented: neither app may import PyQt5/PyQt6/PySide2, and `shared/` (used by both) may
-import PySide6 and nothing else. See `apps/studio/tests/test_binding_purity.py` and
+import PySide6 and nothing else. See `apps/studio/tests/test_studio_binding_purity.py` and
 `apps/autocal/tests/test_binding_purity.py`.
 
 One practical consequence: `pyqtgraph` binds to whichever toolkit it imports first, so a
@@ -109,6 +109,37 @@ mechanically enforced.
 why recording and calibration sampling no longer hang off the UI refresh timer,
 and for the data-reliability fixes that came with it.
 
+### The merge gate
+
+One command runs everything a change must not break, and it is the only check that
+is meant to be unskippable:
+
+```powershell
+powershell -NoProfile -ExecutionPolicy Bypass -File tools\gate.ps1
+```
+
+It runs `tools/lint_gate.py` over the changed files, the full studio suite, the full
+shared suite, and `ui_check.py`; writes each one's output to
+`.scratch/gate/gate-<run-id>/`; and holds the run to three contracts — an **empty**
+`tools/known_failures.txt`, the skip ceilings and collection floors in
+`tools/skip_budget.txt`, and zero findings anywhere. It exits 0 only when all of
+that holds.
+
+The **gate platform is Windows**: the suites render real Qt widgets offscreen, and two
+checks are platform-sensitive ([`docs/test-repair-plan.zh.md`](docs/test-repair-plan.zh.md)
+§3 #11 and #13), so a green Linux run is not the same statement.
+
+An optional `pre-push` hook calls it, so a failing gate blocks the push. It is
+deliberately not installed for you:
+
+```powershell
+git config core.hooksPath .githooks     # enable; `git config --unset core.hooksPath` disables
+```
+
+Day-to-day development still uses targeted test runs
+([`docs/test-execution-plan.zh.md`](docs/test-execution-plan.zh.md)); the gate is what
+runs before a change is committed or handed over.
+
 ## Branding
 
 Window / EXE icon: `shared/resources/branding/logo.png`